1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a jacket utilized during the vulcanization of a belt sleeve and to a manufacturing method utilizing the novel jacket.
2. Background Art
It is common in the art to manufacture power transmission V-belts by initially forming and vulcanizing a belt sleeve, and then cutting a plurality of the belts out of the sleeve.
One such prior art method of manufacture is disclosed in U.S. Pat. No. 3,839,116, to Thomas et al. In Thomas et al, a matrix sleeve 37 is pre-formed with regular, axially spaced, circumferential grooves, corresponding to longitudinal ribs on a completed belt. The matrix sleeve 37 is disposed closely around a drum 44, having an outer surface with a right cylindrical configuration, so that the cylindrical shape of the matrix sleeve is thereby maintained. Belt components are then sequentially built up around the outer surface of the matrix sleeve 37. For example, in FIG. 5, a fabric layer 53, rib stock material 54, elastomeric platform material 55, and cushion material 56 are wrapped consecutively around the matrix sleeve 37, after which a load carrying cord 33 is wound under high tension against the underlying layers to thereby deform the underlying layers partially into the grooves defined by the matrix sleeve 37. As seen in FIG. 6, a top cushion layer 61, an outer layer 62 of elastomeric material, and a fabric layer 63 are wound in turn over the cord 33 to complete the uncured belt sleeve. The uncured belt sleeve is then placed in a vulcanizing unit, identified by Thomas et al as a pot heater, and subjected to steam under controlled temperature and pressure conditions to effect curing and/or vulcanization of the sleeve. The vulcanized sleeve is then cut, by circumferential scoring, to define individual ribbed V-belts.
Belt manufacture, by the structure and method disclosed in Thomas et al, has several drawbacks. First of all, in the high temperature and pressure curing environment, the tensile cords tend to migrate into the lower rubber layer, thereby causing inconsistent and improper positioning of the tensile cords along the belt length. The result of this may be premature failure of the belts.
Another problem contended with in Thomas et al, is that there may be air accumulation between the unvulcanized belt sleeve and rubber matrix during the vulcanization step. This air remains trapped during curing and results in localized pressure on the belt sleeve with resulting irregularities in the final belt shape. Such irregularities detrimentally affect the integrity of the belt.
Further, any air that is entrained in any of the belt components remains trapped therein. During vulcanization, there is no escape route for this air and resultingly the air pockets become permanently molded into the belt components. A sponge-like texture may result, which inherently weakens the belt. The presence of voids or depressions in belts, formed by the Thomas et al method, is common.
A method of belt manufacture similar to that in Thomas et al is disclosed in U.S. Pat. No. 4,409,047, to Brooks. Brooks' disclosure relates to the formation of laterally, rather than longitudinally, extending teeth and additionally to the formation of teeth on both sides of a belt. Brooks, like Thomas et al, utilizes an inner matrix 34 with integrally formed teeth 35 about which belt components are sequentially built. With all belt components in place, a curing jacket 36, with inwardly directed teeth 37, is placed in surrounding relationship with the belt components. The belt sleeve is cured as in Thomas et al.
In Brooks, the problem of air capture is even more vexatious than in Thomas et al's system. In Brooks, the jacket is made from a material that is compatible with and, during the vulcanization process, tends to adhere to, the outer surface of the tension section 23. There is no escape route for air in the component material and, as in Thomas et al, significant amounts of air present between the jacket 36 and tension section 23 during assembly of the jacket 36 become, after curing, an integral part of the belt sleeve, as voids, which weaken the belt.
An alternative, known method of forming transmission belts is disclosed in U.S. Pat. No. 3,822,516, to Huber. Huber teaches the formation of power transmission belts in an inverted orientation. That is, the teeth are formed on the outside of a belt sleeve and, after the individual belts are cut from the belt sleeve, the belts are twisted inside out.
More specifically, Huber provides a cylindrical belt drum 20, having an outer surface with a right cylindrical configuration, to which an expandable tubular member 25 is releasably attached. The transmission belt elements are sequentially built upon the tubular member 25 to form a belt sleeve 24, which is then vulcanized, as in Thomas et al and Brooks, described above. The vulcanized belt sleeve is then ground by means of a rotating wheel to define, in the case of the FIG. 5 belt, a plurality of longitudinally extending belt ribs.
The inverted belt sleeve manufacture method of Huber alleviates the problem of irregular arrangement of tensile cords resulting from the migration of those cords during the vulcanization process, as occurs in both the Thomas et al '116 and Brooks '047 patents. However, air buildup in the Huber structure remains a serious problem. The inverted belt sleeve has an exposed, elastomeric material at its radially outermost surface, which tends to bond with an adjacent curing jacket to fix air pockets in the belt components and prevent escape of any air present between the sleeve 24 and jacket.
Further, there is the same tendency of the sleeve 24 to bond to the tubular member 25 during the vulcanization step with the same detrimental effect--i.e. inconsistent rib shape due to the presence of voids and depressions from trapped air.